The present invention relates generally to reciprocating knife cutters of the type used for cutting pattern pieces or other parts from single ply or low ply sheet materials, such as fabric. More particularly, the present invention relates to a high speed reciprocating knife cutter wherein the knife is driven by an eccentric drive mechanism and a cutting apparatus utilizing such a knife cutter. The invention also relates to a knife sharpener for a cutting apparatus.
A reciprocating knife cutter of a type well-known in the art is shown, for example, in U.S. Pat. No. 4,879,935. The cutter disclosed therein includes a reciprocating knife driven by an eccentric mechanism. The knife is made as a one-piece member having a lower cutting portion supported by guide means for reciprocation along a vertical guide axis, and an upper, resiliently flexible drive portion connected to the drive mechanism. The drive portion flexes laterally in a plane perpendicular to the drive axis of the eccentric mechanism, which permits the knife to be reciprocated along the vertical guide axis. The disadvantage of such a cutter is that a long, flexible knife blade is required which, due to the forces imposed on the flexible drive portion of the blade, has a relatively short service life.
A second type of reciprocating knife cutter well-known in the art is shown in U.S. Pat. No. 2,869,231. The cutter disclosed in this patent also includes an eccentric drive mechanism which reciprocates a knife along a vertical axis. However, in this case the knife is rigid and is driven by a connecting rod which links the top of the knife to the eccentric drive. The inclusion of an extra connecting rod and its associated hardware between the drive and the knife results in a bulky, relatively heavy device which cannot be operated efficiently at high speed. Moreover, the large number of moving parts present in such a device require constant maintenance.
A further disadvantage in many applications associated with both types of cutters described above is that reciprocation of the knife along a strictly vertical axis causes the knife to cut in both its downward and upward strokes as it passes though the sheet material. Cutting during the upward stroke of the knife tends to lift the sheet material from the horizontal surface on which it is supported in a spread condition during the cutting operation. Typically, the sheet material is held down against the support surface by vacuum applied from below. The tendency of the knife to lift the sheet material on the upstroke requires that more vacuum be applied to the material than would otherwise be required in order to insure that the material remains flat against the support surface during the cutting operation.
Cutting apparatus of the type discussed above, as well as cutting apparatus in general, typically have an associated knife sharpener supported directly by the knife cutter. While such an arrangement places the sharpener in close proximity to the cutting blade for periodic sharpening between cutting operations, the sharpener adds weight to the knife cutter making it more difficult to overcome the inertial forces which tend to hinder rapid and precise movement of the cutter with respect to the sheet material being cut.
It is, therefore, an object of the invention to provide a high speed reciprocating knife cutter driven by an eccentric mechanism which does not require either a resiliently flexible knife, or a connecting rod between the knife and the eccentric mechanism.
It is a further object of the invention to provide such a knife cutter which does not tend to lift the sheet material from the support surface during the upstroke of the knife.
It is a still further object of the invention to provide a knife cutter which provides for the use of an easily manipulated, low cost knife.
It is a yet another object of the invention to provide a knife sharpener for a cutting apparatus.